I'm just beginning to design a typeface. So far I've managed to make my way through the alphabet and numbers. Now I'm stumped by the punctuation.

Does anyone have any guide, tips or resources on designing these? I would especially like to know if there is any kind of logic, or best practices for the sizing, placement, spacing and so on of punctuation. A testing text would be nice too especially for the punctuation in use (English is my only language!),